1. Field of the Invention
This invention generally relates to determining an electrical parameter and/or nitrogen content of an insulating film. Certain embodiments relate to determining one or more electrical parameters and the nitrogen content of an insulating film that is imperfectly insulating.
2. Description of the Related Art
Fabricating semiconductor devices such as logic and memory devices typically includes processing a substrate such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, insulating (or dielectric) films may be formed on multiple levels of a substrate using deposition processes such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD). In addition, insulating films may be formed on multiple levels of a substrate using a thermal growth process. For example, a layer of silicon dioxide may be thermally grown on a substrate by heating the substrate to a temperature of greater than about 700° C. in an oxidizing ambient such as O2 or H2O. Such insulating films may electrically isolate conductive structures of a semiconductor device formed on the substrate.
Measuring and controlling such insulating films is an important aspect of semiconductor device manufacturing. A number of techniques are presently available for making such measurements. For example, electrical measurement techniques that rely on physical contact to a conductive electrode on top of an insulating film may be used to determine relevant electrical properties of insulating films using capacitance vs. voltage (C-V) and current vs. voltage (I-V) measurements. Such measurements have a long history and established utility. These measurements, however, require a conductive electrode and a contacting probe. The necessity of direct physical electrical contact is particularly undesirable in many manufacturing situations.
Non-contacting electrical test techniques have been developed to provide electrical capacitance, electrical thickness, and electrical conductivity information about insulating films. Non-contacting electrical measurements of dielectric properties have the unique advantage of providing electrically derived information without the requirement of physical contact to an electrode on top of an insulating film. These techniques typically use an ion generation source such as a corona and a non-contacting voltage measurement sensor such as a Kelvin Probe or a Monroe Probe to determine electrical properties of the films. Examples of such techniques are illustrated in U.S. Pat. No. 5,485,091 to Verkuil, U.S. Pat. No. 6,097,196 to Verkuil et al., and U.S. Pat. No. 6,202,029 to Verkuil et al., which are incorporated by reference as if fully set forth herein. Additional examples of such measurements can be found in “Non-Contact Corona-Based Process Control Measurements: Where We've Been, Where We're Headed,” by Steven R. Weinzierl and Tom G. Miller, Proceedings of the 196th Meeting of The Electrochemical Society, invited presentation, 17–22 Oct., 1999, Honolulu, Hi. and “Uses of Corona Discharges in the Semiconductor Industry,” by R. G. Comizzoli, J. Electrochem. Soc., February, 1987, pp. 424–429, which are incorporated by reference as if fully set forth herein.
One example of a non-contact metrology tool is the Quantox™ system, which is commercially available from KLA-Tencor, San Jose, Calif. This metrology tool is configured to measure gate electrical properties based on the non-contact Kelvin probe measurement principles. Examples of non-contact Kelvin probe measurement principles can be found in the above-referenced article by Weinzierl et al. in addition to “A Contactless Alternative to MOS Charge Measurements by Means of a Corona-Oxide-Semiconductor (COS) Technique,” by R. L. Verkuil and M. S. Fung, Electrochemical Society Extended Abstracts No. 169, Vol. 88–1, 1998, pp. 261–262, “Replacing C-V Monitoring with Noncontact COS Charge Analysis,” by K. D. Catmull, R. G. Cosway, B. A. Letherer, and G. S. Homer, Solid State Technology, June 1998, pp. 203–206, “(Review) Characterization and Production Metrology of Thin Transistor Gate Oxide Films,” by Alain C. Diebold, David Venables, Yves Chabal, David Muller, Marcus Weldon, Eric Garfunkel, Materials Science and Processing 2, 1999, pp. 103–147, and U.S. Pat. No. 4,015,203 to Verkuil, U.S. Pat. No. 4,812,756 to Curtis et al., U.S. Pat. No. 5,485,091 to Verkuil, U.S. Pat. No. 5,767,691 to Verkuil, and U.S. Pat. No. 6,060,709 to Verkuil et al., all of which are incorporated by reference as if fully set forth herein.
One traditional method for measuring equivalent oxide thickness (EOT) involves depositing two different amounts of charge on the film and measuring the corresponding surface voltages. The EOT can be calculated from the ratio of the voltage difference to the charge difference. For non-leaky and relatively good quality films, the deposited charges have stable profiles and stay on the film for a relatively long time. Therefore, the measured amounts of charge and the surface voltages are substantially stable over time. But for leaky films such as very thin oxide films and thin oxynitride films, the charge on the film changes over time. As the time after the charge deposited on the film increases, the charge that is left on the film decreases due to leakage. Therefore, the measured surface voltage also decreases over time. Since the charge deposition gun and Kelvin probe measurement head are at different locations, regardless of how fast the gun or the measurement head moves, there will be measurement time delay. Thus, the measurement time delay and speeds at which the charge deposition gun and the Kelvin probe measurement head move have significant impacts on the measurement results.
Other methods are also proposed to try to correct the leakage effect. Examples of such methods are illustrated in U.S. patent application Ser. No. 10/616,086 entitled “Methods and Systems for Determining a Property of an Insulating Film,” filed Jul. 9, 2003, which is incorporated by reference as if fully set forth herein. One of these methods is commercially available as the ACTIV™ EOT technology, which is incorporated in the Quantox XP system commercially available from KLA-Tencor. This method involves measuring surface voltage as a function of time to characterize the surface voltage decay due to leakage and using the surface voltage decay to correct the EOT. This method works for certain leaky films but for very leaky films, it may not give substantially accurate EOT values and may not have a good correlation to end-of-line C-V measurements.